Pulmonary endothelium is the locus of early structural and functional changes in hyperoxic lung injury. An imbalance between the production of partially reduced oxygen species and their elimination appears to account for the genesis and/or maintenance of such pathology and evidence exists to suggest that such injury may be exacerbated by partially reduced nitrogen species. Nonetheless, in recent years, it is apparent that in many conditions, nitric oxide (NO) may actually limit endothelial cell injury and act as an anti-inflammatory cytoprotective molecule. From recent reports and preliminary data, we hypothesize that iNOS derived NO may be protective to lung endothelium by its potential antiapoptotic effect via posttranslational mechanisms involving S-nitrosylation. Accordingly, the specific aims of this fellowship application are to determine the role of: (1) iNOS-derived NO in affecting pulmonary endothelial cell structure and function in hyperoxia in iNOS-/- mice or in mice that overexpress iNOS in their pulmonary endothelium via somatic gene transfer using a PECAM antibody targeted polyethlyenimine vector containing cDNA to human iNOS; (2) zinc release in NO signaling in the pulmonary endothelium of cultured murine lung endothelial cells and isolated perfused lung using confocal and multiphoton laser scanning microscopy.